Thermal insulating composite structure

ABSTRACT

IMPROVED INTEGRAL, THREE-LAYERED PLASTIC, THERMALLY INSULATING COMPOSITES EACH HAVING AN IMPACT RESISTANT SOLID FACING LAYER OF A MONOVINYL AROMATIC COMPOUND/ALPHAELECTRONEGATIVELY SUBSTITUTED ETHENE COMPOUND INTERPOLYMER SYSTEM, A LAYER OF CELLULAR POLYURETHANE, AND AN ELASTOMERIC INTERLAYER POSITIONED BETWEEN THESE TWO LAYERS.   THE RESULTING COMPOSITES HAVE IMPROVED IMPACT RESISTANCE AS RESPECTS THE SOLID FACING LAYER.

Feb. 16,1971 .1. K. STEVENS THERMAL INSULATING COMPOSITE STRUCTURE FiledApril '22. 1969 3 Sheets-Sheet 1 Ell:

Feb. 16, 1971 J. k. STEVENS 3,563,845

THERMAL INSULATING COMPOSITE STRUCTURE Filed April 22. 1969 3Sheets-Sheet 2 WW M EIEIIII- BY} lqTTalg vgY Feb. 16, 1971 J. K. STEVENS3,563,845

' THERMAL INSULATING COMPOSITE STRUCTURE Filed April 22, 1969 3Sheets-Sheet 5' a v I INVENTOR. JAMES K 5TvNs BYJOAQ. ZdkM United StatesPatent 3,563,845 THERMAL INSULATING COMPOSITE STRUCTURE James K.Stevens, Brimfield, Mass., assignor to Monsanto Company, St. Louis, Mo.,a corporation of Delaware Filed Apr. 22, 1969, Ser. No. 818,459 Int. Cl.B32b /18, 27/40 US. Cl. 161160 5 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND In the art of plastic composities, it has heretofore beenconventional to bond a relatively thick layer of relatively rigid,thermally insulating (or acoustically insulating), cellar, plasticmaterial to a relatively thin layer of solid impact resistant plasticsheeting especially sheeting comprising an interpolymer system ofmonovinyl aromatic compound and an alpha-electronegatively substitutedethene compound. Such composites are useful in many industrial andcommercial applications, including construction materials, refrigeratorcabinets, etc.

Such composites, however, suffer from a severe dis advantage in that thesolid layer apparently can be more readily cracked when rigidly bondedto the cellular layer than in a free, unbonded form. Such cracksoriginate from exterior impacts generally localized in character. Actualcrack propagation through, or in. such solid layer is a relatively lowenergy process while the actual point of crack initiation or formationis usually associated with a relatively high mechanical force.Apparently (though there is no intent to be bound by theory herein) thesolid layer cracks more readily when bonded to the cellular layerbecause then the crack initiation site is in the rela tively morebrittle, more rigid, cellular layer and this site becomes a locus foreasier initiation of cracks than when the solid layer is in a free,unbonded form. The rigidity of the cellular plastic seems to prevent orimpair the shock. r absorbance normally associated with the free,unbonded solid layer.

Heretofore, it has been conventional to overcome such a degradation ofimpact resistance in solid plastic sheeting of such an interpolymersystem when employed in such composites by using thicker or toughersheeting. Such a procedure is disadvantageous since it not only can addappreciably to the cost of a resulting composite, but also it can addundesirable weight to such resulting composite and present subsequentapplication problems.

It has now been discovered, however, that when in such a composite oneuses as the solid layer an interpolymer system of monovinyl aromaticcompound and an alphaelectronegatively substituted ethene compound, andpositions between such solid layer and such cellular layer an iceelastomeric interlayer, the toughness or impact resistance of the solidlayer is surprisingly and unexpectedly improved. This improvement inimpact resistance is achieved without adversely alfecting the desiredgood adhesion characteristics between layers, and, at the same time,does not adversely affect the good structural rigidity characteristicsdesired in such composites. In addition, within composite, the combinedthickness of solid layer and interlayer can be thinner than thethickness of a single thick layer of solid layer used alone and stillachieve a product composite having unexpectedly good impact resistancein the solid facing layer.

Such new three-layer systems find value in a number of industrial andcommercial applications, for example, they are useful as building orcontainer construction materials. When used for instance in theproduction of refrigerator food liners (that is, a refrigerator cabinetand its door), the resulting liners characteristically display superiorshelf-loading capacity and resistance to bulging or oil canning.

SUMMARY This invention relates to thermally or acoustically insulatingpanel-like composites. Each such composite comprises three layers ofmaterial.

A first layer is composed of a cellular polyurethane material havingspaced, generally parallel faces, and having a transverse thickness ofat least about 0.5 cm. (preferably from about 1 to 20 cm.). The cellularmaterial is characterized by having a foam density greater than about0.008 gms./cm. at 23 C. (preferably from about .015 to .06 gram/cm. at23 C.) when individual cells are substantially all gas filled, and byhaving a foam compressive modulus greater than about 5 kg./cm. at 23 C.(preferably from about 20 to 200 kg./cm. at 23 C.). Preferably suchcellular material is substantially closedcelled.

A second layer is composed of an organic, elastomeric polymeric solidhaving spaced, generally parallel faces, and having a transversethickness of from about .01 to 2.5 mm. (preferably from about .02 to 2mm.). The elastomeric solid comprises a saturated or unsaturated rubberwhich, when in a layered form as indicated is characterized by having anapparent tensile modulus of elasticity of from about 2 to 500 kg./cm. at23 C. (preferably from about 3 to kg./cm. at 23 C.) and by having atensile elongation to fail of at least about 100 percent (preferablyfrom about 500 to 1000).

A third layer is composed of an organic, rigid, polymeric solid havingspaced, generally parallel faces, and having a transverse thickness offrom about .25 to 25 mm. (preferably from about .75 to 3 mm.). The solidcomprises an interployrner system of monovinyl aromatic compound andalpha-electronegatively substituted ethene compound, which, when in thelayered form as indicated, is characterized by having an apparenttensile modulus of elasticity of from about 7000 to 55,000 kg./cm. at 23C. (preferably from about 10,000 to 40,00 kg./cm. by having a tensileelongation to fail of at least about 5 percent at 0 C. (preferably fromabout 7 to 30 percent at 0 C.) by having an independent impact strengthgreater than about 1 kg.-m. falling dart at 2.5 mm. thickness and 23C.(preferably from about 2 to 5 kg.-m, all same conditions).

The second layer is interposed between, and is generally contiguouswith, the first and the third layers in composites of this invention.Also, adjacent faces of said first and said second layers, and adjacentfaces of said second and said third layers, respectively, arecontinuously and directly bonded to one another.

For purposes of this invention, foam density, foam compressive modulus,apparent tensile modulus of elasticity, tensile elongation to fail, andthe like, are each conveniently measured using ASTM Test Procedures orequivalent.

A suitable falling dart impact strength measurement test procedure is asfollows:

A falling dart drop testing apparatus like that described in ASTMD-l709-59T is used. The dart has a 1.5 inch diameter hemispherical headfitted with a 0.5 inch diameter steel shaft 8 inches long to accommodateremovable weights. A pneumatic dart release mechanism is positioned sothat the dart is dropped 26 inches onto the surface of the testspecimen. Then test specimen is clamped and held firmly between steelannular rings with an inside diameter of inches. The clamping mechanismis aligned so that the dart strikes the center of the test specimen. Thetest specimens are preferably 6 inch by 6 inch flat plastic sheets.Specimen thicknesses should not deviate more than 5 percent from thenominal or average thickness.

In a test, the specimen is placed in the clamping mechanism, and thedart is loaded with the weight at which 50 percent failure is expected.Then, the test specimen is impacted with the dart and examined forcracks (failure is designated by any crack in the specimen). A newspecimen is used for each impact. In the event that the specimen fails(or does not fail), one decreases (or increases) the weight inincrements of 0.25 pound until the procedure produces afailure-non-failure (or nonfailure-failure) sequence. The resuls arerecorded and the test is preferably continued until at least 15specimens have been thus tested.

The calculation procedure is as follows:

(A) record the number of impacts tested after the failurenon-failure (ornon-failure-failure) point is reached (B) add together the dart weightsfor the N impacts (W),

(C) divide W by N (W (D) multiply W by the drop height (26") to obtainthe 50 percent fail falling dart impact (F To determine falling dartimpact for composites, the following modified procedure may be used. Thesame dart drop testing apparatus as above is used, except that the darthas a one-inch diameter hemispherical head and the test specimen is notclamped, but is placed on a fiat, hard surface. Test specimens arepreferably 4 inch by 4 inch fiat composites. The procedure andcalculations are described as above.

In this invention, the term cellular polyurethane" has reference to apolyurethane, the apparent density of which is decreased substantiallyby the presence of numerous cells disposed in a generally uniform mannerthroughout its mass. These cells are preferably discrete in thisinvention, and the gas phase of each cell is preferably discrete in thisinvention, and the gas phase of each cell is preferably independent ofthat of the other cells in a given cellular polyurethane layer. Forpurposes of this invention, a cellular polyurethane may have itsindividual discrete cells filled with a material other than air, forexample, a fluorinated hydrocarbon, such as trichlorofiuoromethane, orthe like. The density of a cellular polyurethane employed in the presentinvention is conveniently measured at about 23 C. when individualdiscrete cells are substantially all gas filled.

4 COMPONENTS MATERIALS In general, any cellular polyurethane having theabovedescribed characteristics can be used as the first layer inpreparing the composites of this invention, as indicated above. Suchmaterials are well known to those of ordinary skill in the art ofplastics.

Similarly, and in general, any elastomeric solid having theabove-described characteristics can be used as the second layer inpreparing the composites of this invention as indicated above.

Such an elastomeric solid conveniently comprises a saturated orunsaturated rubber. In general, suitable saturated and unsaturatedrubbers for use in this invention have a glass phase or second ordertransition temperature below about 0 C. (preferably below about 25 C.),as determined, for example, by ASTM Test D-746-52T, and have a Youngsmodulus of less than about 40,000 psi. Examples of suitable rubbersinclude unsaturated rubbers, such as homopolymers or copolymers ofconjugated alkadienes (such as butadiene or isoprene), Where, in suchcopolymers, at least 50 percent thereof is the conjugated alkadiene,ethylene/propylene copolymers, neoprene, butyl rubbers, and the like;and saturated rubbers, such as polyurethane rubbers, silicone rubbers,acrylic rubbers, halogenated polyolefin rubbers, and the like.

A preferred class of rubbers for use in this invention are diene polymerrubbers. Examples of diene polymer rubbers include, for example, naturalrubber having isoprene linkages, polyisoprene, polybutadiene (preferablyone produced using a lithium alkyl or Ziegler catalyst),styrenebutadiene copolymer rubber, butadiene acrylonitrile copolymerrubber, mixtures thereof and the like. Such rubbers include homopolymersand interpolymers of conjungated 1,3-dienes with up to an equal amountby weight of one or more copolymerizable monoethylenically unsaturatedmonomers, such as monovinylidene aromatic hydrocarbons (e.g. styrene; anaralkylstyrene, such as the o-, mand p-methylstyrenes,2,4-dimethylstyrene, the ethylstyrenes, p-tert-butylstyrene, etc.; andalphaalkylstyrene, such as alpha-methylstyrene, alpha-ethylene,alpha-methyl-p-methylstyrene, etc.; vinyl naphthalene, etc.); arhalomonovinylidene aromatic hydrocarbons (i.e. the o-, m-, andpchlorostyrenes, 2,4-dibromostyrene, 2- methyl-4-chlorostyrene, etc.);acrylonitrile, methacrylonitrile; alkyl acrylates (e.g. methyl acrylate,butyl acrylate, 2-ethylhexyl acrylate, etc.); the corresponding alkylmethacrylates, acylramides (e.g. acrylamide, methacrylamide, N-butylacrylamide, etc.); unsaturated ketones (e.g. vinyl methyl ketone, methylisopropenyl ketone, etc.); alpha-olefins (e.g. ethylene, propylene,etc.); pyridines; vinyl esters (e.g. vinyl acetate, vinyl stearate,etc.); vinyl and vinylidene halides (e.g. the vinyl and vinylidenechlorides and bromides, etc.); and the like.

A more preferred group of diene polymer rubbers are those consistingessentially of 75.0 to 100.0 percent by weight of butadiene and/orisoprene and up to 25.0 percent by weight of a monomer selected from thegroup consisting of monovinylidene aromatic hydrocarbons (e.g. styrene)and unsaturated nitriles (e.g. acrylonitrile), or mixtures thereof.Particularly advantageous substrates are butadiene homopolymer or aninterpolymer of 90.0 to 95.0 percent by weight butadiene and 5.0 to 10.0percent by weight of acrylonitrile or styrene.

Another preferred class of rubbers for use in this invention are acrylicrubbers. Typically, such a rubber is formed from a polymerizable monomermixture containing at least 40 weight percent of at least one acrylicmonomer of the formula:

Where R is a radical of the formula:

f z n) and p is a positive whole number of from 4 through 12.

Although the rubber may generally contain up to about 2.0 percent byweight of a crosslinking agent, based on the weight of therubber-forming monomer or monomers, crosslinking may present problems indissolving the rubber in monomers for a graft polymerization reaction(as when one makes an interpolymer system as described in more detailhereinafter). In addition, excessive crosslinking can result in loss ofthe rubbery characteristics. The crosslinking agent can be any of theagents conventionally employed for crosslinking rubbers, e.g.divinylbenzene, diallyl maleate, diallyl fumarate, diallyl adipate,allyl acrylate, allyl methacrylate, diacrylates and dimethacrylates ofpolyhydric alcohols, e.g. ethylene glycol dimethacrylate, etc.

Similarly, in general, any rigid solid plastic having thecharacteristics above described can be used as a third layer in thecomposites of this invention, as indicated above. As used herein, theterminology an interpolymer system of monovinyl aromatic compound andalphaelectronegatively substituted ethenes has reference to:

(A) interpolymers formed by polymerizing a monovinyl aromatic compoundwith an alpha-electronegatively substituted ethene,

(B) interpolymers formed by polymerizing a monovinyl aromatic compound,an alpha-electronegatively substituted ethene, and a conjugatedalkadiene monomer.

(C) mechanical blends of such interpolymers (A) and/or (B) With apreformed saturated or unsaturated rubber (such rubbers being as justabove described), one presently preferred such rubber being one derivedfrom a conjugated alkadiene monomer which is either homopolymerized orcopolymerized with another component, especially a monovinyl aromaticcompound or an alphaelectronegatively substituted ethene, or both,

1D) graft copolymer blends of such interpolymers (A) and/or (B) producedby polymerizing the monomers used to make such interpolymers in thepresence of a preformed saturated or unsaturated rubber (ascharacterized above),

(E) mixtures of (A), (B), (C) and/or (D).

In general, such an interpolymer system has a number average molecularweight (WI ranging from about 20,000 through 120,000, and the ratio ofweight average molecular weight (l 1 to number average molecular weightranges from about 2 through 10.

Optionally, such an interpolymer system may have chemically incorporatedthereinto (as through polymerization) a small quantity, say, less thanabout 2 weight percent based on total interpolymer system weight, of acrosslinking agent such as a divinyl aromatic compound, such as divinylbenzene, or the like. Also optionally, such an interpolymer system mayhave chemically incorporated thereinto (as through polymerization) asmall quantity, say, less than about 2 weight percent based on totalinterpolymer system, of a chain transfer agent, such as an unsaturatedterpene, like terpinolene, an aliphatic mercaptan, a halogenatedhydrocarbon, or the like. Such interpolymer systems and methods fortheir preparation are known to the prior art and do not constitue assuch as part of the present invention.

Suitable monovinyl aromatic compounds for use in such interpolymersystems include styrene (preferred); alkyl-substituted styrenes, such asortho-, meta-, and para-methyl styrenes, 2,4 dimethylstyrene, paraethylstyrene, or alpha-methyl styrene; halogen substituted styrenes,such as ortho-, meta-, and para-chlorostyrenes, or bromostyrenes,2,4-dichlorostyrene; and mixed halogen plus alkyl-substituted styrenes,such as 2-methyl-4-chlorostyrene; vinyl naphthalene; vinyl anthracene;mixtures thereof, and the like. The alkyl substituents generally haveless than five carbon atoms, and may include isopropyl and isobutylgroups.

Suitable alpha-electronegatively substituted ethenes for r use in suchinterpolymer systems include those represented by the generic formula:

where X is selected from the group consisting of CN,

COOR and CONHRg,

R is selected from the group consisting of hydrogen, n zn+1) n 2n) and n2n) 2,

R is selected from the group consisting of hydrogen, and

n is an integer of from 1 through 4, and m is an integer of from 1through 8.

Suitable ethene nitrile compounds of Formula 1 include acrylonitrile(preferred), methacrylonitrile, ethacrylonitrile, 2,4-dicyanobutene-1,mixtures thereof, and the like.

Suitable acrylic compounds of Formula 1 include unsaturated acids, suchas acrylic acid and methacrylic acid; 2,4-dicarboxylic acid butene-l,unsaturated esters, such as alkyl acrylates (e.g. methyl acrylate, ethylacrylate,

butyl acrylate, octyl acrylate, etc.), and alkyl methacrylates (e.g.methyl methacrylate, ethyl methacrylate, butyl methacrylate, octylmethacrylate, etc.); unsaturated amides, such as acrylamide,methacrylamide, N-butyl acrylamide, etc.; and the like.

Suitable conjugated alkadiene monomers for use in such interpolymersystems include butadiene, 3-methyl-l,3 butadiene,2-methyl-1,3-butadiene, piperylene chloroprene, mixtures thereof and thelike. Conjugated 1,3-dienes are preferred.

In interpolymer systems of type (A) above, the amount of chemicallycombined monovinyl aromatic compound typically ranges from about 20 to95 weight percent, and preferably from about 50 to 75 weight percent(based on total weight of such interpolymer), while, correspondingly,the amount of chemically combined alkene nitrile typically ranges fromabout 80 to 5 Weight percent, and preferably from about to 10 weightpercent. Examples of such interpolymer systems includestyrene/acrylonitrile copolymers, styrene/acrylate copolymers, and thelike.

Examples of interpolymer systems of type (B) above include especiallycopolymers of styrene, acrylonitrile, and butadiene. In suchinterpolymers, the relative proportions of each of the monovinylaromatic compound and the alkene nitrile remain as in interpolymersystems of type (A), while the amount of chemically combined conjugatedalkadiene monomer typically ranges up to about 25 Weight percent, andpreferably from about 5 to 20 weight percent (based on total weight ofsuch interpolymer).

These interpolymer systems of types (A) and (B) may, if desired, containup to about 7 percent by weight of one or more other copolymerizableethylenically-unsaturated monomers, such as dialkyl maleates, andfumarates (eg the dimethyl, diethyl, dibutyl, and dioctyl maleates, andfumarates, etc.); conjugated dienes (e.g. butadiene, isoprene, etc.);and the like. Also, if desired, the interpolymers can contain minoramounts, e.g. about 0.05 to 3 percent by weight of a chain transferagent, such as a higher alkyl mercaptan, alpha-methylstyrene dimer,terpinolene, and the like.

Among the preferred interpolymers are those which consist substantiallyof about 20 to 95 percent (preferably about to 85 percent) by weight ofa combined monovinyl aromatic hydrocarbon and about 80 to 5 percent(preferably about 50 to percent) by Weight of combined acrylonitrile,methacrylonitrile, methyl acrylate and/ or methyl methacrylate, andmixtures thereof.

Any interpolymer systems of types (A) or (B) employed in addition to agraft copolymer superstrate (see interpolymer system type (B) usuallyhas a specific viscosity of about 0.04 to 0.15, preferably about 0.07 to0.1 measured as a solution of 0.1 percent of the polymer indimethylformamide at C.

In interpolymer systems of types (C) and (D), the total weightpercentage of rubber present typically ranges up to about 25 weightpercent, and preferably from about 5 to 20 weight percent (based ontotal weight of such a blend). Interpolymer systems of type (D) arepreferred, and a particularly preferred such type is a graft copolymerof styrene and acrylonitrile, for example, on a butadiene based rubber.Other unsaturated or saturated rubbers, however, described above can beemployed in place of, or in addition to, such a diene type rubber.

In interpolymer systems of type (D), an interpolymer of type (B) formsthe graft superstrate while the rubber forms the graft substrate.Although the amount of interpolymer superstrate grafted onto the rubbersubstrate may vary from as little as 10 parts by weight per 100 parts ofsubstrate to as much as 250 parts per 100 parts, and even higher, thepreferred graft copolymers have a superstratesubstrate ratio of about200:100 and most desirably about 300-100z100. With graft ratios above30:100, a highly desirable degree of improvement in various propertiesgenerally is obtained.

The interpolymer systems of type (A) and (B) may be produced by variousknown polymerization techniques, such as mass, emulsion, suspension andcombinations thereof. What ever polymerization process is employed, thetemperature, pressure and catalyst (if used) should be adjusted tocontrol polymerization so as to obtain the desired product interpolymer.If so desired, one or more of the monomers may be added in incrementsduring polymerization for the purposes of controlling viscosity and/ ormolecular weight and/or composition. Moreover, it may be desirable toincorporate low boiling organic, inert liquid diluents during a masspolymerization reaction to lower the viscosity, particularly when arubber is employed. Moreover, the catalyst may be added in increments,or different catalysts may be added at the same time or at differentpoints during the reaction. For eX- ample, when a combinedmass-suspension process is employed, generally oil-soluble catalysts maybe employed; and both low and high temperature catalysts may beadvantageously used in some reactions.

The interpolymer systems of type (C) may be prepared by simple,conventional physical intermixing. Conveniently, one uses startingmaterials in a solid, particulate form, and employs such conventionalequipment as a ribbon blender, a Henschel mixer, a Waring Blendor, orthe like.

The interpolymer systems of type (D) may be prepared, for example, bypolymerizing monomers of the interpolymer in the presence of thepreformed rubber substrate, generally in accordance with conventionalgraft polymerization techniques involving suspension, emulsion or masspolymerization, or combinations thereof. In such graft polymerizationreactions, the preformed rubber sub strate generally is dissolved in themonomers and this admixture is polymerized to combine chemically orgraft at least a portion of the interpolymer upon the rubber substrate.Depending upon the ratio of monomers to rubber substrate andpolymerization conditions, it is possible to produce both the desireddegree of grafing of the interpolymer onto the rubber substrate and thepolymerization of ungrafted interpolymer to provide a portion of thematrix at the same time. A preferred method of preparation involvescarrying out a partial polymerization in a bulk system with the rubberdissolved in a mixture of the ethene monomers and vinyl aromaticmonomers, followed by completion of the polymerization in an aqueoussuspension system.

Blends may be prepared by blending latices of a graft copolymer and aninterpolymer and recovering the polymers from the mixed latices by anysuitable means, e.g. drum-drying, spray-drying, coagulating, etc.Preferably, they are prepared by simply oomalaxating a mixture of theinterpolymer and the hydroxylated graft copolymer at an elevatedtemperature for a period of time sufiicient to provide an intimatefusion blend of the polymers. Blends of graft copolymer and interpolymercan be prepared by simply blending the two polymers together onconventional plastics working equipment, such as rubber mills,screw-extruders, etc.

As suggested above, interpolymer systems of monovinyl aromatic compoundand alpha-electronegatively substituted ethenes most desirably employedin the present invention are those wherein at least a portion of such aninterpolymer system has been so prepared in the presence of rubber as tocause some degree of chemical combination to occur between the rubberand remaining interpolymer system components. Typically, a small amountof the superstrate interpolymer is not in chemical combination with therubber substrate because of the lessthan-100 percent grafting efliciencyof conventional graft copolymerization reactions.

It will be appreciated that any given third layer used in this inventiongenerally comprises at least about 50 weight percent of an interpolymersystem of monovinyl aromatic compound and alpha-electronegativelysubstituted ethenes with the balance up to 100 weight percent thereofbeing another polymer, such as a polyvinyl chloride, a polycarbonate, apolysulfone, a polyphenyleneoxide, a polyamide, or the like, provided,of course, the particular combination of polymers employed in a thirdlayer has, when formed into such a given third layer, physicalcharacteristics such as described above. Preferably, a third layercomprises at least weight percent of such interploymer system.

It will also be appreciated that any given first layer, second layer, orthird layer can have incorporated thereinto minor amounts (say, up toabout 15 weight percent total of any given such layer of conventionaladjuvants', organic or inorganic fillers, fiame retardants,plasticizers, antioxidants, stabilizers, and the like so as to enhance agiven set of properties physical, chemical, economic, or the like) in aparticular product of the invention. For example, a first, second orthird layer could have up to 10 percent plasticizer, up to 15 percentpigment, up to 5 percent stabilizer, and up to about 5 percentmiscellaneous other additional additives, such as antioxidants, fillers,'bactericides, fungicides, etc., all as those skilled in the art willappreciate.

METHODS OF FABRICATION While conventional methods are used in making thecomposite products of this invention, it will be appreciated that somemethods are presently more convenient and preferred.

Thus, one perferred method of fabrication commences with a performedabove-described third layer in sheet form such as is done byconventional plastic forming procedures as those skilled in the artappreciate. If a three-dimensional shaped configuration is desired in aparticular composite product to be manufactured, then it is convenientto make such third layer in the particular configuration desired, as byconventional vacuum forming injection molding technology, or the like,all as those skilled in the art appreciate.

Next, one face of such sheet (for example, the outer face, as when arefrigerator interior cabinet is being made) is coated with a solutionor dispersion of the above-described second layer. The polymericmaterial consituting this layer is conveniently applied in solution ordispersion form by spraying (preferred) painting,

dipping, or the like, and thereafter volatiles (the liquid carrier) areremoved by evaporation. Solutions or dispersions of such a polymericmaterial are well known to those of ordinary skill in the art and arenot part of this invention; the liquid medium can be aqueous and/ororganic. Convenient concentrations of dispersed or dissolved polymericmaterial therein typically range from about 10 to 90 weight percent(based on total weight), preferably from about 30 to 70. Preferably, theliquid medium used is one which will not cause the third layer to crazeor be damaged before such medium evaporates.

Finally, the exposed face of the second layer is coated with theabove-described first layer. The thermoset foam material comprising thisthird layer in this preferred method of fabrication is produced bypositioning the two layered structure fabricated as just described in amold chamber or equivalent and then depositing on such second layerwithin the mold chamber the chemicals which will generate in situ the'desired thermoset closed-celled cellular plastic layer, and allowing thefirst layer to form in the mold chamber. Afterwards, depending on theparticular composite being formed, the mold chamber may be removed toseparate the completed composite of this invention.

Observe that the above-preferred fabrication method requires no adhesivesystem(s) to bond together the second to the first layer and the thirdto the second layer. The forming procedure produces a product in whichthe individual contiguous layers are mutually interbonded.

While the above-described preferred fabrication procedure involves twolayers generated in situ at time of composite fabrication, those skilledin the art will appreciate that the first, the second and the thirdrespective layers can each be separately formed independently of eachother and then bonded together to form a desired composite structure ofthis invention.

For example, one can commence fabrication of a composite of thisinvention with a preformed above-described third layer. One face of thisthird layer is brushed or coated with a solvent, for example, ahydrocarbon solvent such as toluene, hexane, dimethylformamide, or thelike. Then against the so-solvent brushed surface is pressed a preformedsecond layer. The solvent evaporates but before this occurs, the surfaceof the second layer is sufficiently softened and partially dissolved tocause bonding between adjacent surfaces of the third layer and the firstlayer. Thus, in this way are laminated together a performed first layerand a performed second layer. Over the exposed face of the second layeris conveniently coated the chemical system which will form the firstlayer. For example, in the manner as just described above (e.g. thefirst layer is again formed in situ).

In another method of lamination a preformed third layer is selected anda preformed thermoplastic second layer is selected and the two arebonded together directly by heat and pressure, the heat and pressurebeing applied against the two sheets while in face-to-face engagementwith one another for a time sufficient to effect lamination directlybetween the two adjacent surfaces. Then, over the exposed face of thesecond layer, the first layer is formed in situ, for example, asdescribed above. Although any convenient heat lamination conditions canbe employed, it is convenient to use temperatures ranging from about 100to 250 F. and pressures of from about 500 to 3000 p.s.i. (or even higherpressures, as desired) applied for times ranging from about A to 10minutes.

Another fabrication procedure involves using a preformed third layer.One coats one face of such third layer with a thin layer of an organicsolvent liquid, such as an aromatic hydrocarbon, an aldehyde, a ketone,etc. at an application rate of from about /2 to grams per sq. ft.Thereafter, one presses against the so'moistened face of the third layera preformed second layer using a pressure ranging from about 15 to 50p.s.i. applied for times of from about /2 to 5 minutes.

Another fabrication procedure involves using a pre formed third layerand a solvent solution or dispersion of the second layer (for example,about a 10 weight percent solids solution or dispersion in an organicsolvent or liquid as just indicated). The third layer is then coatedwith such solution so as to produce a layer after solvent or carrierliquid evaporation which is of the appropriate thickness to constitute asecond layer of the invention. The solution or dispersion is applied tothe third layer by any conventional technique, including painting,casting, spraying, etc. Usual drying times can range up to about 24hours at room temperatures through drying times can be accelerated usingelevated temperatures, as those skilled in the art will appreciate.

In general, any convenient and suitable method of fabrication can beused to make the composite of the present invention.

DESCRIPTION OF THE DRAWINGS Composites of the present invention and apreferred method of construction thereof are most particularlyillustrated in the attached drawings wherein:

FIG. 1 is an isometric view of a corner region of one embodiment of acomposite of this invention, some parts thereof broken away and someparts thereof shown in section;

FIG. 2 is a diagrammatic illustration showing another embodiment of acomposite of the present invention used as a construction element in thefabrication of a building wall;

FIG. 3 illustrates a first step in the manufacture of another embodimentof a composite of the present invention wherein the composite issuitable for use as a food liner in a refrigerator cabinet;

FIG. 4 illustrates a second step in such manufacture;

FIG. 5 illustrates a third step in such manufacture;

FIG. 6 illustrates another step in such manufacture;

FIG. 7 illustrates a final step in such manufacture;

FIG. 8 illustrates the construction of the resulting refrigerator foodliner showing an elevational view of a corner thereof, some partsthereof broken away, and some parts thereof shown in section; and

FIG. 9 is a vertical sectional view taken along the line 9-9 of FIG. 8.

Turning to these drawings, there is seen in FIG. 1 a view of oneembodiment of a composite member of this invention designated in itsentirety by the numeral 10. Composite 10 is seen to comprise a firstlayer 11, a second layer 12, and a third layer 13 integral with oneanother in face-to-face engagement. Layer 11 is composed of a cellularplastic such as polyurethane foam, or the like; layer 12 is composed ofan elastomeric solid such as styrene/butadiene copolymer, or the like;and layer 13 is composed of a semi-rigid plastic such as acrylonitrile/butadiene/styrene, or the like. Individual thicknesses of theserespective layers can range as described hereinabove.

In FIG. 2 is seen a composite 14 similar to composite 10 except thatcomposite 14 has two third layers 19 and 20. Each third layer 19 and 20is bonded to a different second layer 17 and 18, respectively. In turn,each second layer 17 and 18 is bonded to a different opposed face of afirst layer 16. Layers 13, 19, and 20 are made by ex trusion or thelike; layers 12, 17 and 18 are sprayed on as from aqueous dispersions orthe like, followed by evaporation of carrier liquid, and layers 11 and16 are foamed in place using fixturing not shown.

As shown, both composite 10 and composite 14 are in sheet form, and theyare usable in a number of ways. For example, composite 14 is shown inFIG. 2 being used as the interior portion of a building wall. Thus,composite 10 is secured to studs 21 (only one shown in dotted lines)such as a conventional wooden so-called two-by-four, or the like as withan adhesive system such as a conventional phenolic or polyvinyl alcoholadhesive or the like or other means. The exterior portion of this wallis composed of tongue and groove boards 22 or the like, as desired.Composite 14 thus avoids the use of separate insulation means betweeninterior portion and exterior portion of a Wall.

FIGS. 3-9 illustrate production of a refrigerator food linerincorporating a composite structure of this invention. Thus, in FIG. 3is shown a third layer (such as a sheet ofacrylonitrile/butadiene/styrene plastic or the like) which has beenformed into the box-like configuration shown, for example, in a singleoperation by vacuum forming in a molding machine. This third layercomprises entire inside wall portions of a refrigerator cabinet, suchthird layer being herein designated in its entirety as wall member 23.This wall member 23 can have formed therein protrusions, depressions, orthe like (all not shown) to facilitate or accommodate mounting ofshelves, etc. therein in the fully assembled, functional refrigerator,as those skilled in the art will appreciate.

The exterior surface regions 24 of third layer 23 are spray coated (seeFIG. 4) with a solution or dispersion containing the elastomeric solidcomprising a second layer of a composite structure of this invention (asfrom the nozzle 26 of a spray gun not shown), thereby to deposit on theexterior surface regions 24 a second layer 27 (of styrene/butadiene orthe like). The liquid used as the carrier for such solution ordispersion evaporates to leave the layer 27 which is adhered and bondedcontinuously to surface regions 24.

Next, the double layered laminate construction comprising wall member 23and second layer 27 is assembled with exterior wall member 28 for arefrigerator cabinet (see FIG. Exterior wall member 28 is conventionallypreformed in a separate operation (not shown) and is conventionallycomposed either of sheet-metal (such as steel or the like), or ofplastic (such as the same plastic used in wall member 23). If thelatter, then the inner surfaces of exterior wall member 28 can, ifdesired, be coated (not here shown) with second layer 27. Conveniently,exterior wall member 28 has a separate back wall panel 29. The doublelayered laminate construction comprising wall member 23 and second layer27 is moved into exterior wall member 28 through the aperture formedwhen back Wall panel 29 is removed, after which back wall panel 29 issecured to the adjoining portions of the remainder of exterior wallmember 28 by any convenient means, such as screws, adhesives, etc. (notshown) extending between panel 29 and inturned flanges 35 on suchremainder of member 28, as those skilled in the art will appreciate. Theexterior wall member 28 is adapted to have hinges (not shown) and a doorlatch (not shown) mounted thereon exteriorly so that a door (not shown)can be hung across the front regions of the assembly thereby to providea complete refrigerator cabinet. Exterior wall member 28 is outfittedwith a compartment or space 30 in its lower region to accommodate therefrigerator cooling mechanism (not shown) including compressor, coils,electric motor, and associated components.

The assembly of exterior wall member 28, and double layered laminateconstruction comprising wall member 23 as the third layer and secondlayer 27 is now positioned in a supporting frame assembly designated inits entirety by the numeral 32 (see FIGS. 6 and 7). Frame assembly 32includes interior and exterior supporting side wall members 33 and 34,respectively, as well as interior and exterior supporting rear wallmembers 36 and 37, respectively, which cooperate together and functionto brace, respectively, adjacent wall portions of wall member 23 andoutside surface portions of exterior wall members 28. Suitable bracingand hinge means, generally not shown, are employed in frame assembly 32to secure frame assembly 32 demountably against such surface portions.Such bracing is desirable and sometimes necessary (depending uponpressures developed) to support the assembly comprising wall members 23and 28 and associated elements during in situ production of a firstlayer in the void space 38 now existing between Wall member 23 and wallmember 28. In this space 38 is injected as through a nozzle 39 a liquidchemical composition which chemically interacts with itself to form aclosed cell foam, thereby creating a first layer 41 (see FIGS. 8 and 9)and forming a composite structure of this invention. FIGS. 8 and 9 showthe resulting construction and are intended to help make clear theinter-relationships between the various layers one with the other. Afterfirst layer 41 is formed, the frame assembly 32 is removed and the nowcompleted refrigerator food liner is used in the manufacture of acomplete refrigerator.

EMBODIMENTS The following examples are set forth to illustrate moreclearly the principles and practice of this invention to one skilled inthe art and they are not intended to be restrictive but merely to beillustrative of the invention herein contained.

Example 1 A sheet of acrylonitrile/butadiene/styrene plastic materialtermed ABS herein and available commercially under the trademark Lustran461 from Monsanto Company measuring approximately 1 ft. x 2 ft. x milsare prepared by extrusion and cutting. Each sheet has an apparentmodulus of elasticity of about 340,000 p.s.i. at 23 C., and elongationto fail of about 25 percent at 23 C. and an independent impact strengthgreater than about 35 ft./lb. falling dart (at 2.5 mm. thickness and 23C.), each such sheet in this example constitutes a third layer suitablefor use in a composite of this invention, as such terminology is usedherein.

One face of each such sheet is spray coated with a dispersion. The sprayapparatus used is a so-called De Vilbiss spray gun equipment with afiuid tip designated CGA- IS-FF employing about 30 pounds air pressure.This dispersion is in aqueous latex form and contains about 74 weightpercent of a copolymer comprising 75 weight percent butadiene and 25weight percent styrene (available commercially under the trademarkPliolite 5352 from the Goodyear Tire and Rubber Co.). This dispersion isapplied at a rate such that, after application to the sheet surface andafter evaporation of the carrier liquid (e.g. Water) therefrom, there isleft on the sheet surface bonded thereto a generally uniform coating ofthe styrene/butadiene copolymer. This coating has a thickness of about.002 inch and has an apparent modulus of elasticity of about 200 p.s.i.at 23 C. and an elongation to fail of about 600 percent at 23 C. Thiscoating constitutes a socalled second layer in a composite of thisinvention as this terminology is used herein.

Each such laminate of third layer and second layer is now placed in analuminum mold whose void space measures approximately 1 ft. x 2 ft. x 1/2. This mold with the laminate therein is now heated to a temperatureranging from l40 F., and a sufficient quantity of a mixed urethane foamprecursor is injected into the mold void so as to produce in the moldvoid a final polyurethane foam layer having a foam density of about 2.5pounds per ft. As the foam expands and cures in the mold void, the foambonds to the second layer. Each such foamed layer so formed also has anapparent compressive modulus greater than about 800 p.s.i. at 23 C. Eachfoam layer so formed in this example constitutes a first layer in acomposite of this invention as this terminology is used herein.

There is thus formed a three-layered composite of this invention. Suchcomposite comprises a first layer, a second layer and a third layer. Thecompleted composite is cut into 4" x 4" squares for impact testing. Eachsuch product square undergoes a falling dart impact test as follows.

A modified falling dart method is used, as follows: A

dart with a 1" diameter nose is weighted and dropped onto the ABS sheetfacing of the composite from a height of 3 feet. The amount of weight onthe dart is adjusted (see above described procedure for measuringfalling dart impact) to obtain the 50% fail point.

Each resulting such composite has a thickness of about 1 /2" and afalling dart impact strength (measured against the third layer) of about13.1 ft./lbs. at F.

This composite is a great improvement over the falling dart impact of1.2 ft./ lbs. obtained on a composite panel prepared in the same moldusing the same ABS facing and the same urethane foam, but Without theelastomeric interlayer.

the preformed second layer is pressed thereagainst using a pressure ofabout 30 psi. applied for a time of about 1 min. In Example 12, thesecond layer is formed by casting the second layer over one face of thethird layer. The third layer is coated With about 10 mils of anelastomer-containing organic solution (10% solids) and permitted to dryat room temperature for 24 hours. In all these examples, the third layeris preformed. For each example, the composition of the third layer, ofthe second layer, and of the first layer, respectively, are eachdesignated in the column entitled Type and the number in each example insuch respective column for each of the respective layers is explained ina legend following Table 1.

TABLE 1 Third layer Second layer Tensile Indefail pendent Tensileelonfalling Layer Thickmodulus gation dart thickness, 23 0., 23 0., 230. Method of ness, Type (mm) kgJcm. percent (kg/m) Type application mm.

Example Number:

2 (1) 1.5 25,000 30 3.3 .05 (1) 2. 25, 000 30 5. 5 05 (2) 1. 5 20,000 405. 5 05 (1) 1. 5 25, 000 30 3. 3 .05 (1) 1. 5 25, 000 30 3. 3 05 1) 1. 525, 000 30 3. 3 05 (1) 1. 5 25, 000 30 3. 3 5) 05 (1) 1.5 25,000 30 3.3(7) d0 .05 (1) 1.5 25,000 30 3.3 (s) H at laminated--. .025 (1) 1.525,000 30 3.3 (9) Solventlaminated. .25 (1) 1.5 25,000 30 3.3 (10) Cfilm (1) 1. 5 25, 000 3. 3 1) 1. 5 25, 000 30 3. 3 1 1. 5 25, 000 30 3.3 1 1. 5 25, 000 30 3. 3 1 1. 5 25, 000 30 3. 3

Second layer First layer Tensile Composite fail Com- Tensileelonpressive Composite falling, modulus gation modulusThickdartimpact,kg./ml.

23 C 23 0., Density, 23 0., ness, kgJcm. percent Type g./cm. kg.lem. cm.23C. 180.

28 500 (12) .04 70 3. s 3. 0 1. 9 28 500 (12) .04 70 3. 8 5. 0 3. 1 28500 (12) 04 70 3.8 5. 0 3. 0 23 500 (12) 07 130 3.8 3. 0 1. 3 500 12) 0470 3. s 2.8 1. s 14 900 (12) 04 70 3. s 2. 5 1. 7 18 500 (12) 04 70 3. s2. 7 1. 3 14 550 (12) 04 70 3. 8 2. 7 1. 7 21 700 (12) .04 70 3.8 3.0 1. 1 11 1, 100 (12) 04 70 3.8 3. 3 1. 3 11 1, 100 (12) 04 70 3. s 2.5 1. 5 23 800 (12) 04 70 3. 3 2. 3 1. 5 12) 04 70 3. s 0. 3 0. 2 23 50013) 055 105 3. s 2. 9 1. 7 23 500 (14) 09 150 3. s 3. 0 1. 8 28 500 (12)04 70 2. 5 2.8 1. 7

Examples 2 through 16 Legend of Layer Chemical Composition (the numberbein as desi nated in Table 1 Additional composites of thls inventionare prepared. g g The Composition,respfictivelyflf thirdlayensewndlayer,(1) An acrylonitrile/butadiene/styrene plastic material a first y the Py Charactenstlcs all as available commercially under the trademarkLustran lineated in Table 1 below. In all such composites, the firstfrom Monsanto c This material is layer is produced by following theprocedure in Example duced in Sheet form by extrusion. 1 abOYe, that 15to the first layer, fi m g (2) An acrylonitrile/butadiene/styreneplastic material Such Place Over the Second layerlm i elscn availablecommercially under the trademark Lustran m Examp 1e In all these exam-p8 Secon ayer Is 762 from Monsanto Company. This material is pro spraycoated 1n the manner described 1n Example 1 above v duced in sheet formby extrusion. except for Examples 10, 11, and 12. In Example 10, the

h (3) A copolymer formed from percent butadiene and second layer 1spreformed and 1s heat laminated to t e 30 t t .labl O r ian in the formthird layer using a temperature of about 150 F., a pres- 7 Percen SYrene aval F if mine C llfd d sure of about 1500 p.s.i., the temperatureand the pressure of an aqueous latePf as a We1g tpercent 1 S ISIPeTSIOTIbeing applied for a timc of about 5 min In Example 11, under the tradedesignation FRS221 from the Firestone the second layer is laminated tothe third layer by the Tire and Rubber Co. I I method of partialsolvation. Thus, one face of the third (4) A polymer of polybutadieneavailable commercially layer is coated uniformly with a thin layer oftoluene and m the form of an aqueous latex as a Weight percent 15 solidsdispersion under the trade designation FRS2004 from the Firestone Tireand Rubber Co.

() A polymer of 2-chloro-butadiene-l,3 (sometimes called Neoprene)available commercially in the form of an aqueous latex as a weightpercent solids dispersion under the trademark Vultex 3N-2D from theGeneral Latex Co.

(6) An acrylic rubber polymer available commercially in the from of anaqueous latex as a weight percent solids dispersion under the trademarkVultacryl A115 from the General Latex Co.

(7) A urethane rubber polymer available commercially in the form of anaqueous latex as a weight percent solids dispersion under the tradedesignation E-502 from the Wyandotte Co.

(8) A urethane rubber film available commercially under the trademarkPerflex from the Union Carbide Co.

(9) A styrene/butadiene block copolymer available commercially in theform of an aqueous latex as a weight percent solids dispersion under thetrademark Thermoplastic 125 from the Shell Oil Co.

(10) A 10 weight percent solution of (9) in toluene.

(11) A styrene/butadiene block copolymer available as a solution underthe trademark Kraton 101 from the Shell Oil Co. (a five weight percentsolution of the polymer in a 50/50 toluene xylene solution).

(12) A polyurethane foam available in the form of a foamable liquidsystem under the trademark Vultafoam 16F702 from the General Latex andChemical Corp. The foam formed from this material is a rigid thermosetclosed celled trichlorofluoromethane blown structure.

(13) A polyurethane foam available in the form of a foamable liquidsystem under the trademark Selectrofoam 6403 from Pittsburgh PlateGlass. The foam formed from this material is a rigid thermoset closedcelled trichlorofluoromethane blown structure.

(14) A polyurethane foam available in the form of a foamable liquidsystem under the trademark Vultafoam 15-L-204 from General Latex andChemical Corp. The foam formed from this material is a rigid thermosetpartially open-celled, carbon dioxide blown structure.

EXAMPLE 17 Refrigerator cabinet The following example is described inreference to FIGS. 39. In FIG. 3 is shown the inside refrigeratorcabinet food liner wall member 23, which has been vacuum formed from a.250 inch thick extruded sheet of ABS plastic (Lustran 461). The averagewall thickness in the part is .090 inch. The food liner dimensions are37 /2 x 20 /2. Wall member 23 constitutes a third layer of a compositestructure of this invention.

The exterior surface regions 24 of wall member 23 are spray coated (FIG.4) with a 75 percent butadiene, 25 percent styrene copolymer aqueouslatex having 74 percent weight solids (Goodyears Pliolite 5352) toproduce the second layer of a composite structure of this invention.After evaporation of the liquid carrier, the solid, elastomeric layer 27is left on the wall member.

Next, the double layered construction comprising wall member 23 andlayer 27 is assembled together with an exterior wall member 28 insupporting frame assembly 32. The exterior wall member 28 is preformedin a separate operation and is composed of 22 gauge mild steel. Theexterior wall member 28 has an inturned flange 31 which is one inchwide, upon which the out-turned one inch flange 25 of the interior foodliner 23 is sealed. The space between the interior and exterior cabinetsis 1 /2 inches wide. The separate exterior back panel 29 seats againstcabinet flange 35 on the exterior wall member 28.

The distance between the two walls is about 1 /2 inches and thecalculated volume is about 2.9 cubic feet. Hot

air (160 F.) from a so-called D&W Hopper Dryer manufactured by so-calledThoreson-McCosh Company is blown into the air space between outer andinner cabinets for approximately two hours. This gives a pre-heattemperature of 130140 F. to the liner before foaming.

Urethane foam is metered and mixed using a laboratory scale so-calledAdmiral -2FSP two component machine whose output is 9 pounds per minute.Vultafoam 16F702 with a free rise density of 2.0 lbs./ft. is used.Fifteen percent excess foam is used to insure filling. Thus, thein-place density is 2.3 lbs./ft. The time needed to fill is about 44seconds.

During foaming, the foam is distributed down the sides and across theback of the food liner. The pour is programmed so that the sides andback receive approximately 11 seconds of pour time and the top andbottom receive approximately 5 /2 seconds.

After introduction of the foam, the back cabinet panel and back supportpanel are put into place and the support clamps latched. Rise and cureof the foam are allowed to proceed at room temperatures.

The resulting refrigerator food liner after removal from the supportingframe 37 constitutes a composite construction of this invention. Thefood liner can be conventionally used in the manufacture of arefrigerator cabinet.

The impact strength of the inner cabinet is 15 ft./ lbs. measuredagainst the third layer by falling dart impact.

This is a significant improvement over the 2 ft./lbs. recorded for acabinet prepared in the same manner using the ABS facing and the sameurethane foam but without the second layer of this invention.

What is claimed is:

1. A plastic, composite, thermally insulating, panellike member, oneface of which has impact resistance, said member comprising:

(A) a first layer of a cellular polyurethane having spaced, generallyparallel faces and having a transverse thickness of at least about 0.5cm., said cellular plastic being characterized by:

(1) having a density of at least about .008 gm./

cm. at 23 C. when individual cells are substantially all gas filled, and

(2) having a compressive modulus greater than about 5 kg./cm. at 23 C.,

(B) a second layer of an elastomeric, organic, polymeric solid plastichaving spaced generally parallel faces and having a transverse thicknessof from about .01 to 2.5 mm., said elastomeric, solid plastic beingcharacterized by:

(1) having a tensile modulus of elasticity of from about 2 to '500kg./cm. at 23 C., and

(2) having a tensile elongation to fail of at least about 100 percent at23 C.,

(C) a third layer of semi-rigid, solid plastic having spaced, generallyparallel faces and having a transverse thickness of from about .25 to 25mm., said rigid, solid plastic being characterized by:

(1) having a tensile modulus of elasticity of from about 7000 to 55,000kg./cm. at 23 C.

(2) having a tensile elongation to fail of at least about 5 percent at23 C.,

(3) having an independent impact strength greater than about 1 kg./cm.falling dart (at 2.5 mm. thickness and 23 C.), and

(4) comprising an interpolymer system of monovinyl aromatic compound andelectronegatively substituted acrylic compound,

(D) said second layer being interposed between, and generally contiguouswith, said first and said third layers, and

(E) adjacent faces of said first and said second layers, and adjacentfaces of said second and said third layers, respectively, beingcontinuously directly bonded to one another.

2. The composition of claim 1 wherein said first layer 1 7 1 8 iscomposed substantially of a closed-celled cellular poly- ReferencesCited urethane 3. The composite of claim 2 wherein said first layer isUNITED T S PATENTS composed substantially of an open-celled cellularpoly- 3091946 6/1963 Keshng 161 161X urethane. 5

4. The composite of claim 1 wherein said second layer ROBERT F. BURNETT,Primary Examiner comprises a styrene/butadiene copolymer.

5. The composite of claim 1 wherein said third layer POWELL AsslstantExammer is composed substantially of a graft copolymer blend of U S C1XR a monovinyl aromatic compound, an alpha-electronega- 10 tivelysubstituted ethene, and a conjugated alkadiene. 52-309; 117--104; 15679,244; 16l44, 190; 26445

